試題詳解

14. A 3.0-kg block is on a horizontal surface. The block is at rest when, at t = 0, a force (magnitude P = 12 N) acting parallel to the surface is applied to the block causing it to accelerate. The coeflicient of kinetic friction between the block and the surface is 0.20. At what rate is the force P doing work on the block at t = 2.0 s? Take g = 10 m/s².
(A)54W
(B)48W
(C)42W
(D)59 W
(E) 24 W